Some internal combustion engines can vary operation of one or more cylinders between different modes of operation depending on the operating conditions of the engine or other vehicle systems. As one example, at least a portion of the engine cylinders can be transitioned between a spark ignition (SI) mode and a homogeneous charge compression ignition (HCCI) mode in response to the level of torque requested by the vehicle operator. As another example, the number of firing cylinders may be reduced, under some conditions, by the use of cylinder deactivation, in order to conserve fuel and improve efficiency of the engine, while the number of firing cylinders may be increased where a greater amount of engine torque is requested. In this way, advantages associated with each mode of operation can be achieved while reducing or eliminating the disadvantages of each of the modes by selectively utilizing mode transitions.
However, the inventors herein have recognized some issues relating to the above approaches. Specifically, in some conditions, engine transitions between different modes of operation may cause torque transients or discontinuities that can result in increased longitudinal acceleration of the vehicle and/or excitation of the vehicle driveline. As such, the mode transitions may, in some cases, be perceived by the vehicle operator, may increase mechanical wear of vehicle components, or may increase the likelihood of mechanical malfunction, due to the torque transients occurring during the transition.
In at least one approach described herein, at least some of the above issues may be addressed by a method of operating an engine having a plurality of cylinders, the method comprising transitioning the engine from a first mode to a second mode; and temporarily adjusting an amount of torque produced by a cylinder of the engine for at least one cycle responsive to a difference in an amount of torque produced by a previous firing cylinder and a subsequent firing cylinder. In this way, one or more cylinders of the engine may be adjusted before or after the transition responsive to the torque signature of the first mode and the second mode, thereby reducing torque transients that may result in excitation of the driveline including the transmission and/or increased longitudinal acceleration of the vehicle. Note that the different modes of operation may include a change in combustion mode, number of firing cylinders, and/or the number of strokes performed per cycle.
As another approach described herein, at least some of the above issues may be addressed by a method of operating an engine having a plurality of cylinders, wherein the engine is configured to provide torque to a drive wheel of a vehicle via a transmission, the method comprising transitioning the engine from a first mode to a second mode; and adjusting an amount of torque produced by at least one of a last firing event of a cylinder in the first mode and a first firing event of a cylinder in the second mode responsive to a condition of the transmission. In this way, the engine may be controlled during transitions between different modes of operation in response to a condition of the transmission such as the selected gear ratio or the amount of slip provided by a transmission clutch, for example.
As yet another approach described herein, at least some of the above issues may be addressed by a method of operating an engine having a plurality of cylinders, the method comprising transitioning at least one cylinder of the engine from a first mode to a second mode; and temporarily adjusting a peak amount of torque produced by one of a last firing cylinder of the first mode and a first firing cylinder of the second mode for at least one cycle responsive to a difference between a first quantity of firing cylinders in the first mode and a second quantity of firing cylinders in the second mode. In this way, the engine may be controlled during transitions between modes having different quantities of firing cylinders, such as may be provided by a variable displacement engine.
It should be appreciated that the several approaches provided by the above summary are non-limiting examples of the various concepts that will be further described in the detailed description and are not intended to define the scope of the present application or claimed invention.